Thirty-four documented cases of familial amyotrophic lateral sclerosis from 14 families were evaluated by physical examination and review of medical records and autopsy material and records. Two forms can be differentiated on the basis of duration of course: one lasting one-five years and the other 10-25 years. In addition, there may be subtypes within groups separated by pathologic findings: the presence or absence of degenerative changes in the posterior columns, Clarke's column, and spinocerebellar tracts in addition to changes classically found in the anterior horn cells and corticospinal tracts. HL-A typing was done on 35 individuals including five who were affected, but results were uninformative.